ok i have some LED's i plan to use to accent my stereo and car. the problem is this. 12volts seems to bee too much for them when hooked to 1.5-3.0volt batteries they act fine but when hooked to a 9volt battery they heat up bad then stop working all together.
so i assume that a 12volt battery well deffinatly eat them up.
bassicaly my question is what do i need to wire in before the LED's to lower the voltage to them? or what do i need to do if not wire something inline.
thanks as always for any advise.
Replies (29)
swez on 02/28/2004 11:38:08
I just did one of these deal in my Dad's truck. The Ford emblem in the grill, I installed 3 mini lamp to light up the logo when the parking lights are on.
These were pretty small diodes (but bright) and had a load resistor inline with the + side of the LED to bring down the voltage to usable levels. The first 3" behind the LED were shrink tubed, but I did see a slight buldge where the load resistor was installed.
Got them at Auto Zone in a 3 pack. Try these as they already have the resistor built in. They also came in several colors. Pretty cheap to.
Swez
uochronos on 02/28/2004 13:33:50
already bought the LED's got a good deal for them... just wasnt sure if a resistor was all i needed. last thing i want to do is install them all and have to re do it hehe.... how do i find out what size resistor i need or would the guy at radio shack know? ya i know radio shack components suck but i dont know any other place to go thats not online
cplkittle on 02/28/2004 16:00:04
If I remember correctly, wiring them in series is the same as wiring a sub in series. You get higher resistance, and a voltage drop. 3 LEDs in a series will only get 4v each (12/4) on a DC circuit. Try wiring them this way and connecting them to the 1.5 volt battery... If I am correct, they will not be as bright as they were individually.
uochronos on 02/28/2004 16:01:44
ahh good idea i do plan to hook them up in strings of 4 anyway...
swez on 02/28/2004 19:41:32
The resistance value is determined by the voltage supply VS lamp internal resistance. (voltage needs) The higher the load resistance, the less light the LED will emit.
Also, if you do go with a stringer of series wired lamps, if one goes out, they all go out... like the old style christmas lights.
I think you can measure a diodes forward bias resistance, then calculate the resistor value needed for each lamp. It may be trial and error or mathmatically determined by ratios.
Up to you, but CPL is correct in his assertions of a series string. Each lamp will get 1/4 the voltage applied. (using 4 per string) A 12 volt source... you get 3 volts per lamp.
Swez
uochronos on 02/29/2004 03:13:34
3 volts should be about right because the specs on them says 2-3volts i just found thaty:)... and one going out isnt a big deal they last for just about ever and only 40cents each so just replace all 4 if i can easily see which one went out. just about everywhere i'm putting them i wanted to use 4 anyway so that works out well. and i well get load resistors where i need it... ok if wireing them in series gets me less voltage to each one what does paralell do then?
cplkittle on 02/29/2004 09:53:13
they get the same voltage as the source (12v).
That is how you wire lights in a house, so they do not dim. There is a greater pull (in larger wattage applications) so a larger wire is needed the more you have. In this case that is not a factor.
swez on 02/29/2004 13:16:37
If you go parallel, each LED will need a resistor. That resistor will need to be 3-4X the LED load resistance to get ~3 volts from a 12 volt source. Does not have to be a high wattage resistor either.... a 1/4 watt resistor should be fine as very little current will flow here due to high resistance.
Swez
uochronos on 02/29/2004 17:10:08
ok so if i use a resistor i measure the LED natural resistance then get how big of a resistor?
lets assum that the LED has a resistance of 1ohm just for this conversation. if that was true then what size resistor would i need?
swez on 02/29/2004 17:42:44
You will need a 3.0 ohm resistor that dissapates ~1/4 watt.... That's 3 volts (25%) to lamp and 9 volts (75%) blead off by the resistor.
I think I said 4 times diode in the last post, but 3 is good and easy to work the numers. If the diode is 1,000 ohms, then a 3.3Kohm resistor in series should do it etc.
If this is for your car... you have a working voltage of ~13.5 volts. So you can make a test with a 3*X and 4*X resistor to see which one illuminates to your taste.
X is the Resistance value of the diode and you need a 3-4:1 ratio here to get adequate voltage to the lamps
Swez
uochronos on 02/29/2004 23:55:09
ok cool sounds like i'm set to do it then.... thanks for the help... the guy at radio shack looked at me last night like i was speaking chinnese when i told him what i was doing...
cplkittle on 03/1/2004 11:40:47
lol, I get that alot.. I went to Circuit city to buy RCA connectors. just the ends, and they guy kept asking me why. I told him I needed an RCA that was 6" long, and didn't want to pay $20 for it, so I was going to make my own. Long story short.. I showed him my setup, and my custom box. Now I am building a custom box for him (the installer) and the salesman that work in the car audio department. When you start asking alot of technical questions to younger salesmen, it blows their mind.
ttocs on 03/1/2004 12:48:50
it is not hard to impress the cc or bb boys.... BOYS being the key word...
ah swez, measuring a doides resistance will only get you a very small resistance forward biased, reversed biased will get you nothing... Isn't a single 3 ohm resistor is gonna get you alot of current? 12v/3ohm=4amps if the voltage loss across the diode is neglected(.7v).....
swez on 03/1/2004 14:24:43
Right you are ttocs... and no, am not advocating a 3 ohm resistor... but a 3X resistance value of the diode resistance. This is a lamp diode too, so resistance across the light junction may show a more accurate read on its true resistance.
Not having the "DCR" spec of this device makes things a bit more guess work than specifics. But the ratio of resistance to diode lamp resistance is correct. To get ~3.0 vdc to the diode, (from 12 volt source), need 75% more series resistance than the diode to get proper diode voltage.
Swez
PS How was your bike treck? Grooling event I bet???
ttocs on 03/1/2004 17:45:39
ok, that makes sence...
I still think an led however has no to little resistance on it. What we need to worry about it the current then. I would wire 4 in series as mentioned before, with a 1.5 k ohm resistor also inline. If you want them brighter, try a lower resistance... You could use a pot.(variable resistor) to get the brightness you need...
uochronos on 03/1/2004 18:27:07
4 inline well work for most of my application but there are 2 or 3 places i want to mount just one. and your right they have almost no resistance just tested one. ok assumeing it has no resistance how big of a Resistor well i need?
swez on 03/1/2004 19:18:52
Well, we can reverse engineer a bit here. We know there is a resistance value of the lamp when lit. What that will be is not easily determined unless you do a voltage drop test between the power souce and the diode or a current (ampere draw) test with a meter and regulated power supply or 12 volt battery.
The easy way would be to string 4 devices in series, then read the current flowing through the circuit. We know the source is 12 volts, we dont know resistance yet. But if we can determine current draws from the string, we cacn use Ohm' Law to figure out what R total is and divide by 4. That would give us net resistance per device.
OHM'S LAW:
P = IxR
E = E/IxR
We know E =12 volts
We can determine I (current) buy measuring with ampmeter
Once we know E & I, we can figure out R total and R/4 = net resistance of each bulb E/I =R of 4 lamps in series.
Once R of each bulb is determined, a 3*R resistor will be the right choice for parallel installs off each lamp.
Got an ammeter? Am sure a low range one will be fine. The probes are in series with power supply and load.
Pos12 volts....wwww....wwww....wwww....wwww....+probe/ meter.. to - probe of meter to.... - on battery Neg this will net current flow number of the entire circuit.
Got it?
Swez
uochronos on 03/1/2004 19:24:38
yep seems easy enough i well try that tomarow thanks
swez on 03/1/2004 20:03:55
You bet!
ttocs on 03/1/2004 22:54:36
let us know what happens.. I say they blow. It has been too long since school.... I would have known then.......
swez on 03/2/2004 05:48:03
Hehe, yeah.... same here A LONG TIME and all my engineering books are back in MI. But this should work as we know the working voltage, just have to determine 1 more variable (R or I) to noodle this one out.
Swez
uochronos on 03/2/2004 17:58:28
ok i broke my multimeter so i can test so i'm going the long rought i bought a 10k ohm resistor, a 68ohm, and a 100ohm. the guy at radio shack said it should be a 100ohm or 10k ohm. and another guy told me he used a 70ohm on his so i well just see which one works best and adjust till i find one that works the resistors are only 15 cents each so its not big loss. unless someone knows how i can find out without using a ampmeter. also if you wanna see the specs for these LEDs to better help me. there at www.superbrightleds.com and i bought the red leds that are 8000 and 30degrees viewing angles.
swez on 03/2/2004 19:45:24
Looks like:
Emax is: 2.6 volts
I draw: 20ma (.02A.)
R= E/I = 130 ohms per device
Load resistor: 450-500 ohms
If I have this right, looks like your resistor should be ~400-500 ohms range in series w/ 1 lamp off a 12 volt source. (470 is recommended)
Bone head! Read the specs: THINK
Avoid damage to LEDS by soldering for no longer than 3 seconds with 700° iron.
LED life expectancy is based on current and temperature. You can expect our LEDS to last approximately 100,000 hours at 20 ma with ambient temperature of 20° C.
DO NOT use LEDS without a current limiting resistor in series with the LED. The forward voltage rating is TYPICAL and can vary from part to part, so while some LEDS may work fine just connected to a battery of the proper voltage, other will be overdriven and destroyed. ALWAYS USE A RESISTOR IN SERIES WITH THE LED OR LEDS
*** Use a 1/8th watt or larger resistor soldered to the anode of the led and connect the +12 to the resistor. The chart below shows you the forward current for each color led with a single led in series with a 470 ohm resistor connected to 12 VDC.
Swez
PS The specs for the resistor are on the site and all details on how to use in 12 volt applications. READ THE INSTRUCTIONS !!! GRIN
uochronos on 03/3/2004 00:08:57
lol even after you told me it was there took me like 15 minutes to find the instructions lol. well looks like i'm set then just have to go grab some resistors of that size thanks again.
swez on 03/3/2004 08:35:00
Yes, it took me several minutes to find it and I figured it would be there somewhere... just had to dig a bit. Now we know... 470 ohms is a standard resistor as is 500. Either will work fine, but 500 ohms will dim the light a tad more.
Swez
uochronos on 03/8/2004 04:06:02
Ok last question for this thread if the LEDs take 470ohm resistors which they do could i use 430ohm resistors? bassicaly i plan to be hooking up lots of leds for my car and friends cars and can either pay .99 for 5 470ohm resistors or i can get a great deal from a place with surplus 430ohm resistors for 10$ for 1000 resistors... so you can see my want to save eheh
swez on 03/8/2004 10:57:58
Yes, a 430 ohm will work. A bit more voltage to the LED and may shorten the life of same... but hey, within the 10% tolerance level of a typical resistor.
If your new 430's have a 5% TOLERANCE or better, this would be a good thing.
Here is a link to 10 packs of 470 ohm, 1/2/watt, 5% tolerance flame proof resistors. This might be good for your application and only 4 - 5 cents each, depending on quantity.
http://www.partsexpress.com/pe/showdetl.cfm?&User_ID=19418890&St=9439&St2=-74350945&St3=-34204888&DS_ID=3&Product_ID=4&DID=7
Swez
ttocs on 03/8/2004 11:02:48
flame proof, take all our fun away........
uochronos on 03/8/2004 15:42:37
thanks guys but after i posted last night went on ebay found a whole case of 470ohm resistors for 9.00 so i have a 1000 resistors on the way hehe.
so i assume that a 12volt battery well deffinatly eat them up.
bassicaly my question is what do i need to wire in before the LED's to lower the voltage to them? or what do i need to do if not wire something inline.
thanks as always for any advise.
Replies (29)
swez on 02/28/2004 11:38:08
I just did one of these deal in my Dad's truck. The Ford emblem in the grill, I installed 3 mini lamp to light up the logo when the parking lights are on.
These were pretty small diodes (but bright) and had a load resistor inline with the + side of the LED to bring down the voltage to usable levels. The first 3" behind the LED were shrink tubed, but I did see a slight buldge where the load resistor was installed.
Got them at Auto Zone in a 3 pack. Try these as they already have the resistor built in. They also came in several colors. Pretty cheap to.
Swez
uochronos on 02/28/2004 13:33:50
already bought the LED's got a good deal for them... just wasnt sure if a resistor was all i needed. last thing i want to do is install them all and have to re do it hehe.... how do i find out what size resistor i need or would the guy at radio shack know? ya i know radio shack components suck but i dont know any other place to go thats not online
cplkittle on 02/28/2004 16:00:04
If I remember correctly, wiring them in series is the same as wiring a sub in series. You get higher resistance, and a voltage drop. 3 LEDs in a series will only get 4v each (12/4) on a DC circuit. Try wiring them this way and connecting them to the 1.5 volt battery... If I am correct, they will not be as bright as they were individually.
uochronos on 02/28/2004 16:01:44
ahh good idea i do plan to hook them up in strings of 4 anyway...
swez on 02/28/2004 19:41:32
The resistance value is determined by the voltage supply VS lamp internal resistance. (voltage needs) The higher the load resistance, the less light the LED will emit.
Also, if you do go with a stringer of series wired lamps, if one goes out, they all go out... like the old style christmas lights.
I think you can measure a diodes forward bias resistance, then calculate the resistor value needed for each lamp. It may be trial and error or mathmatically determined by ratios.
Up to you, but CPL is correct in his assertions of a series string. Each lamp will get 1/4 the voltage applied. (using 4 per string) A 12 volt source... you get 3 volts per lamp.
Swez
uochronos on 02/29/2004 03:13:34
3 volts should be about right because the specs on them says 2-3volts i just found thaty:)... and one going out isnt a big deal they last for just about ever and only 40cents each so just replace all 4 if i can easily see which one went out. just about everywhere i'm putting them i wanted to use 4 anyway so that works out well. and i well get load resistors where i need it... ok if wireing them in series gets me less voltage to each one what does paralell do then?
cplkittle on 02/29/2004 09:53:13
they get the same voltage as the source (12v).
That is how you wire lights in a house, so they do not dim. There is a greater pull (in larger wattage applications) so a larger wire is needed the more you have. In this case that is not a factor.
swez on 02/29/2004 13:16:37
If you go parallel, each LED will need a resistor. That resistor will need to be 3-4X the LED load resistance to get ~3 volts from a 12 volt source. Does not have to be a high wattage resistor either.... a 1/4 watt resistor should be fine as very little current will flow here due to high resistance.
Swez
uochronos on 02/29/2004 17:10:08
ok so if i use a resistor i measure the LED natural resistance then get how big of a resistor?
lets assum that the LED has a resistance of 1ohm just for this conversation. if that was true then what size resistor would i need?
swez on 02/29/2004 17:42:44
You will need a 3.0 ohm resistor that dissapates ~1/4 watt.... That's 3 volts (25%) to lamp and 9 volts (75%) blead off by the resistor.
I think I said 4 times diode in the last post, but 3 is good and easy to work the numers. If the diode is 1,000 ohms, then a 3.3Kohm resistor in series should do it etc.
If this is for your car... you have a working voltage of ~13.5 volts. So you can make a test with a 3*X and 4*X resistor to see which one illuminates to your taste.
X is the Resistance value of the diode and you need a 3-4:1 ratio here to get adequate voltage to the lamps
Swez
uochronos on 02/29/2004 23:55:09
ok cool sounds like i'm set to do it then.... thanks for the help... the guy at radio shack looked at me last night like i was speaking chinnese when i told him what i was doing...
cplkittle on 03/1/2004 11:40:47
lol, I get that alot.. I went to Circuit city to buy RCA connectors. just the ends, and they guy kept asking me why. I told him I needed an RCA that was 6" long, and didn't want to pay $20 for it, so I was going to make my own. Long story short.. I showed him my setup, and my custom box. Now I am building a custom box for him (the installer) and the salesman that work in the car audio department. When you start asking alot of technical questions to younger salesmen, it blows their mind.
ttocs on 03/1/2004 12:48:50
it is not hard to impress the cc or bb boys.... BOYS being the key word...
ah swez, measuring a doides resistance will only get you a very small resistance forward biased, reversed biased will get you nothing... Isn't a single 3 ohm resistor is gonna get you alot of current? 12v/3ohm=4amps if the voltage loss across the diode is neglected(.7v).....
swez on 03/1/2004 14:24:43
Right you are ttocs... and no, am not advocating a 3 ohm resistor... but a 3X resistance value of the diode resistance. This is a lamp diode too, so resistance across the light junction may show a more accurate read on its true resistance.
Not having the "DCR" spec of this device makes things a bit more guess work than specifics. But the ratio of resistance to diode lamp resistance is correct. To get ~3.0 vdc to the diode, (from 12 volt source), need 75% more series resistance than the diode to get proper diode voltage.
Swez
PS How was your bike treck? Grooling event I bet???
ttocs on 03/1/2004 17:45:39
ok, that makes sence...
I still think an led however has no to little resistance on it. What we need to worry about it the current then. I would wire 4 in series as mentioned before, with a 1.5 k ohm resistor also inline. If you want them brighter, try a lower resistance... You could use a pot.(variable resistor) to get the brightness you need...
uochronos on 03/1/2004 18:27:07
4 inline well work for most of my application but there are 2 or 3 places i want to mount just one. and your right they have almost no resistance just tested one. ok assumeing it has no resistance how big of a Resistor well i need?
swez on 03/1/2004 19:18:52
Well, we can reverse engineer a bit here. We know there is a resistance value of the lamp when lit. What that will be is not easily determined unless you do a voltage drop test between the power souce and the diode or a current (ampere draw) test with a meter and regulated power supply or 12 volt battery.
The easy way would be to string 4 devices in series, then read the current flowing through the circuit. We know the source is 12 volts, we dont know resistance yet. But if we can determine current draws from the string, we cacn use Ohm' Law to figure out what R total is and divide by 4. That would give us net resistance per device.
OHM'S LAW:
P = IxR
E = E/IxR
We know E =12 volts
We can determine I (current) buy measuring with ampmeter
Once we know E & I, we can figure out R total and R/4 = net resistance of each bulb E/I =R of 4 lamps in series.
Once R of each bulb is determined, a 3*R resistor will be the right choice for parallel installs off each lamp.
Got an ammeter? Am sure a low range one will be fine. The probes are in series with power supply and load.
Pos12 volts....wwww....wwww....wwww....wwww....+probe/ meter.. to - probe of meter to.... - on battery Neg this will net current flow number of the entire circuit.
Got it?
Swez
uochronos on 03/1/2004 19:24:38
yep seems easy enough i well try that tomarow thanks
swez on 03/1/2004 20:03:55
You bet!
ttocs on 03/1/2004 22:54:36
let us know what happens.. I say they blow. It has been too long since school.... I would have known then.......
swez on 03/2/2004 05:48:03
Hehe, yeah.... same here A LONG TIME and all my engineering books are back in MI. But this should work as we know the working voltage, just have to determine 1 more variable (R or I) to noodle this one out.
Swez
uochronos on 03/2/2004 17:58:28
ok i broke my multimeter so i can test so i'm going the long rought i bought a 10k ohm resistor, a 68ohm, and a 100ohm. the guy at radio shack said it should be a 100ohm or 10k ohm. and another guy told me he used a 70ohm on his so i well just see which one works best and adjust till i find one that works the resistors are only 15 cents each so its not big loss. unless someone knows how i can find out without using a ampmeter. also if you wanna see the specs for these LEDs to better help me. there at www.superbrightleds.com and i bought the red leds that are 8000 and 30degrees viewing angles.
swez on 03/2/2004 19:45:24
Looks like:
Emax is: 2.6 volts
I draw: 20ma (.02A.)
R= E/I = 130 ohms per device
Load resistor: 450-500 ohms
If I have this right, looks like your resistor should be ~400-500 ohms range in series w/ 1 lamp off a 12 volt source. (470 is recommended)
Bone head! Read the specs: THINK
Avoid damage to LEDS by soldering for no longer than 3 seconds with 700° iron.
LED life expectancy is based on current and temperature. You can expect our LEDS to last approximately 100,000 hours at 20 ma with ambient temperature of 20° C.
DO NOT use LEDS without a current limiting resistor in series with the LED. The forward voltage rating is TYPICAL and can vary from part to part, so while some LEDS may work fine just connected to a battery of the proper voltage, other will be overdriven and destroyed. ALWAYS USE A RESISTOR IN SERIES WITH THE LED OR LEDS
*** Use a 1/8th watt or larger resistor soldered to the anode of the led and connect the +12 to the resistor. The chart below shows you the forward current for each color led with a single led in series with a 470 ohm resistor connected to 12 VDC.
Swez
PS The specs for the resistor are on the site and all details on how to use in 12 volt applications. READ THE INSTRUCTIONS !!! GRIN
uochronos on 03/3/2004 00:08:57
lol even after you told me it was there took me like 15 minutes to find the instructions lol. well looks like i'm set then just have to go grab some resistors of that size thanks again.
swez on 03/3/2004 08:35:00
Yes, it took me several minutes to find it and I figured it would be there somewhere... just had to dig a bit. Now we know... 470 ohms is a standard resistor as is 500. Either will work fine, but 500 ohms will dim the light a tad more.
Swez
uochronos on 03/8/2004 04:06:02
Ok last question for this thread if the LEDs take 470ohm resistors which they do could i use 430ohm resistors? bassicaly i plan to be hooking up lots of leds for my car and friends cars and can either pay .99 for 5 470ohm resistors or i can get a great deal from a place with surplus 430ohm resistors for 10$ for 1000 resistors... so you can see my want to save eheh
swez on 03/8/2004 10:57:58
Yes, a 430 ohm will work. A bit more voltage to the LED and may shorten the life of same... but hey, within the 10% tolerance level of a typical resistor.
If your new 430's have a 5% TOLERANCE or better, this would be a good thing.
Here is a link to 10 packs of 470 ohm, 1/2/watt, 5% tolerance flame proof resistors. This might be good for your application and only 4 - 5 cents each, depending on quantity.
http://www.partsexpress.com/pe/showdetl.cfm?&User_ID=19418890&St=9439&St2=-74350945&St3=-34204888&DS_ID=3&Product_ID=4&DID=7
Swez
ttocs on 03/8/2004 11:02:48
flame proof, take all our fun away........
uochronos on 03/8/2004 15:42:37
thanks guys but after i posted last night went on ebay found a whole case of 470ohm resistors for 9.00 so i have a 1000 resistors on the way hehe.
Copyright ClubKnowledge 2009 * All Rights Reserved
